Field of the Invention
The present invention relates to an optical coherence tomography apparatus as represented by, for example, an ophthalmologic device, avid to a control method for the optical coherence tomography apparatus and a non-transitory tangible medium.
Description of the Related Art
Currently, there are various types of ophthalmologic devices using an optical device. For instance, as an optical device for observing an eye, there are used various devices such as an anterior ocular segment imaging device, a fundus camera, and a confocal laser scanning ophthalmoscope (scanning laser ophthalmoscope: SLO). In particular, an optical tomographic imaging apparatus, which performs optical coherence tomography (OCT) utilizing an interference phenomenon of multi-wavelength light, is an apparatus capable of obtaining a tomographic image of a sample with high resolution. For this reason, the optical tomographic imaging apparatus is becoming an indispensable apparatus as an ophthalmologic device tor a specialist of retina in the outpatient field. In addition, the optical tomographic imaging apparatus is used not only for ophthalmologic use but also for an endoscope or the like. This apparatus is hereinafter referred to as “OCT apparatus”. The OCT apparatus is widely used for acquiring a tomographic image of a retina of a fundus or a tomographic image of an anterior ocular segment such as a cornea of an eye to be inspected in ophthalmologic diagnosis or the like.
The OCT apparatus is capable of splitting measuring light having low coherence into reference light and measuring light, and irradiating an object to be inspected with the measuring light to cause return light from the object to be inspected to interfere with the reference light, to thereby measure a layer of the object to be inspected from spectrum information of interference light. As to the current OCT apparatus, a spectrum domain OCT (SD-OCT), which can acquire information on the object to be inspected in a depth direction from the above-mentioned spectrum information on interference light, is used in general. In the present invention, the SD-OCT apparatus is hereinafter referred to simply as “OCT apparatus”.
The OCT apparatus, which is capable of acquiring a high resolution tomographic image by scanning a sample with measuring light, acquires a two-dimensional image by one-dimensional scanning of a specific area with the measuring light. Further, a three-dimensional image (volume data) is acquired by repeating the one-dimensional scanning for acquiring the two-dimensional tomographic image while shifting a position.
Here, it is known that the retina of a human eye includes a plurality of layers. In ophthalmological diagnosis, radiographic image interpretation of the layer structure is made or a state of a lesioned part is checked based on the volume data. In addition, in volume image data of the retina, in order to check a state of a lesioned part, it is effective to display a tomographic image, to analyze a layer structure image of the retina, and to display a layer thickness graph, a layer thickness map, or the like (see Japanese Patent Application Laid-Open No. 2012-071113). Further, it is also effective to compare a calculated layer thickness with layer thickness data of a healthy eye (normative data base (NDB)) for checking a state of a lesioned part.
However, it is known that when the spectrum information is used for acquiring a tomographic image of the object to be inspected, there is generated a folded image of a normal tomographic image with respect to a position called a gate at which a measuring optical path and a reference optical path are equal to each other, due to characteristics of Fourier transform performed in the calculation thereof. Further, when the tomographic image of the object to be inspected crosses the gate position, the normal tomographic image and the folded tomographic image are overlaid to become a double image.
When the tomographic image is a double image, it is difficult to distinguish a layer structure of the sample by image analysis. For this reason, layer thickness analysis data of the double imaging area, may not be appropriately provided to a user. Therefore, in Japanese Patent Application Laid-open No. 2011-092290, there is disclosed an ophthalmologic device in which a warning is issued when a tomographic image of an object to be inspected is formed outside an appropriate photographable area in order to prevent photographing an image in a state where the folded image is overlaid on the normal tomographic image.
However, even when the ophthalmologic device disclosed in Japanese Patent Application Laid-open No. 2011-092290 is used, the user may perform photography in a state where a folded image is generated. This is because the user may perform photography with a focused part intentionally positioned to be close to the gate position because the tomographic image becomes more blurred due to a decrease of signal intensity or the like as the focused part becomes distant from the gate position. In addition, because the retina of a human eye does not have a flat plans but has a curved shape, the tomographic image may cross the gate position to generate the folded image in an area distant from the focused part. Further, when the retina has a large curvature due to excessive myopia or the like, it may be difficult to photograph the entire retina in a state in which no folded image is generated.